php计算剩余时间的自定义函数

public function gettime($time_s,$time_n){
$time_s = strtotime($time_s);
$time_n = strtotime($time_n);
$strtime = '';
$time = $time_n-$time_s;
if($time >= 86400){
return $strtime = date('Y-m-d H:i:s',$time_s);
}
if($time >= 3600){
$strtime .= intval($time/3600).'小时';
$time = $time % 3600;
}else{
$strtime .= '';
}
if($time >= 60){
$strtime .= intval($time/60).'分钟';
$time = $time % 60;
}else{
$strtime .= '';
}
if($time > 0){
$strtime .= intval($time).'秒前';
}else{
$strtime = "时间错误";
}
return $strtime;
}